This invention relates to the growth of monocrystalline bodies and more particularly to the production of monocrystalline closed-end structures such as domes.
Various methods have been developed for growing monocrystalline bodies from a melt. The present invention pertains to an improvement in growing crystalline bodies from a melt according to what is called the edge-defined, film-fed, growth technique (also known as the EFG process).
In earlier U.S. Pat. Nos. 3,915,662 (Labelle and Cronan) and 3,915,656 (Mlavsky and Pandiscio) techniques have been described for growing a closed end tube by the EFG method. Such tubes can be formed of numerous oxides by crystallizing the oxide, for example sapphire, from a columnar meniscus in contact with a wetted die surface under controlled growth conditions. Such closed end sapphire tubes can then be machined to form sapphire domes which are particularly useful in making electromagnetic domes. Some additional work has been described, for example, by Borodin et al "Journal Of Crystal Growth" 82 (1987) pages 89-84. This article shows hollow cones having rough interior and exterior shapes formed by a technique not fully described in the Borodin et al article. It may involve the technique described by Antonov etc., in Izvestia Akadimil Nauk SSR, Seriya Fizicheskay Vol. 49 No. 12 PP 2595-2292, 1985 wherein a growing tube is rotated over a wetted shaping element whose surface is smaller than the diameter of the tube. In the Antonov system only a small portion of the growing tube is adjacent the shaping element. Additionally, Labelle U.S. Pat. No. 3,846,082 describes a crystal growing technique where a small portion of a dome surface is formed by rotating a crystal partially around an axis of rotation above the wetted surface for which the crystal is grown. Labelle makes no effort to orient this crystal and the position of the axis substantially above the wetted surface prevents formation of a hemispherical dome.